1. Field of the Invention
The present invention relates to a method for obtaining high purity nickel powder from a nickel ammine sulfate complex solution and briquettes prepared by pressing the powder.
Particularly, the present invention can be applied to a treatment of an in-process intermediate solution generated from a nickel hydrometallurgical process.
2. Description of the Related Art
A method for industrially producing nickel powder using a hydrometallurgical process includes a method for producing nickel powder by dissolving a raw material in a sulfuric acid solution followed by removing impurities to obtain a nickel sulfate solution, adding ammonia to the resulting nickel sulfate solution to form an ammine complex of nickel, and feeding hydrogen gas into the produced nickel ammine sulfate complex solution to reduce nickel.
For example, Japanese Patent Laid-Open No. 2005-240164 describes a process for producing nickel powder by adding an iron compound as seed crystals during the reduction reaction to precipitate nickel on the iron compound, and the problem is that iron derived from the seed crystals is mixed into the product.
Further, a method for obtaining nickel powder using a reducing agent other than hydrogen gas has also been proposed.
For example, Japanese Patent Laid-Open No. 2005-240164 discloses nickel powder which is inexpensive, is excellent in weatherability, has low electric resistance in a state where it is kneaded with a resin, reduces initial electric resistance and electric resistance in use, can be stably used over a long period of time, and is suitable as conductive particles for a conductive paste and a conductive resin, and a method for producing the nickel powder.
The nickel powder disclosed in Japanese Patent Laid-Open No. 2005-240164 contains 1 to 20% by mass of cobalt with the balance consisting of nickel and unavoidable impurities, comprises secondary particles in which primary particles are aggregated, and has an oxygen content of 0.8% by mass or less. The reference teaches that cobalt is contained only in the surface layer part of the secondary particles, and the cobalt content in the surface layer part is preferably 1 to 40% by mass. When the nickel powder is intended to be obtained by the disclosed production method, cobalt will coexist. Therefore, the method is not suitable for an application in which nickel and cobalt are present in combination, for example, in a nickel oxide ore; these metals are separated; and each metal is intended to be economically recovered as high purity metal.
Further, Japanese Patent Laid-Open No. 2010-242143 provides a method for producing metal powder by a liquid phase reduction method that is improved so that a particle aggregate may be hardly produced.
The method for producing metal powder comprises a first step of dissolving a metal compound, a reducing agent, a complexing agent, and a dispersant to prepare an aqueous solution containing metal ions derived from the metal compound, and a second step of adjusting the pH of the aqueous solution to reduce the metal ions with the reducing agent to precipitate the metal powder.
However, this production method requires high cost since an expensive chemical is used, and is not economically advantageous for applying the method to a process operated on a large scale as the above nickel smelting.
Although various processes for producing nickel powder have been proposed as described above, a method for producing high purity nickel powder using industrially inexpensive hydrogen gas has not been proposed.
In such a situation, the present invention intends to provide a production method for producing coarse particles of high purity nickel powder from a nickel ammine sulfate complex solution using fine nickel powder and using industrially inexpensive hydrogen gas.